The invention relates to a circuit arrangement for an anti-locking braking system for motor vehicles.
A known circuit arrangement (FR-A 2,250,098) of such a type relates to an anti-lock braking system for motor vehicles. Inter alia, it has an image correlator in which beams emitted from a light source are thrown onto the road and the reflected beams pass via a diffraction grating to two photo-electric receivers. When the vehicle is moving, the output signals of these receivers have a frequency component which is evaluated. At a vehicle speed which would lead to locking of the wheels and hence to the vehicle skidding in the event of sudden braking, the evaluation leads to the brakes of the vehicle being operated automatically and, in addition, to a suitable warning advice for the driver optionally being activated.
In contrast, normal anti-lock braking systems identify the start of the locking of a wheel in that the rotation speeds of the various wheels differ from one another in a typical manner. However, a difficulty with such a circuit arrangement is that it must also be able to identify that all the wheels are locked simultaneously when the vehicle is not yet stationary, that is to say when it is skidding over the ground beneath it with the wheels locked.